Definitions of institution
a long-established law or custom
Critics have attacked the plans as an assault on the institution of marriage.
an established society or official organization with an important role in society (eg a school or a hospital); a large company
The Catholic Church, based in Rome and headed by the Pope, is the oldest institution in the western world.
the action of instituting something
I am advised that there is sufficient admissible evidence to support the institution of criminal proceedings.